A display industry generally includes not only process industries of display modules such as LCD, PDP and OLED but also their forward industries such as TV, notebook, PC monitor, PDA and cellular phone and their backward industries such as component materials and manufacture equipment.
A display module has a device configuration composed of a panel, a black matrix, and a color filter. A white surface light input from a backlight unit passes through pixels. The panel controls the white surface light according to a signal voltage of individual pixels input from a driving circuit unit to realize a color image. In addition, the black matrix is formed among pixels of the color filter to isolate lights emitted from pixels such that the lights do not interfere with each other. Also, the black matrix absorbs light input from outside such that the light is not reflected. The color filter is a resin film including dyes or pigments of three basic colors (R, G, B) such that a light passing through a liquid crystal has a color.
In recent, cost reduction is coming into an essential issue in the electronic industry fields and flat plate display fields including LCD, and the ink-jet printing technology is applied in pattern formation of the color filter for the cost reduction. That is to say, the ink jet printing technology allowing simplification of a production procedure and design of a large-sized product substitutes for existing technologies in aspect of cost reduction so as to manufacture a pattern of color filter in an easy and cheap way, and its application is more expanded from the display field.
Generally, the ink-jet printing is a non-contact patterning technique that injects solution or suspension into droplets of several to several ten pl (Pico Liter) through fine nozzles, and it allows printing into a resolution of several ten micrometers.
This ink-jet printing technology is applied in various ways from the display field such as PDP, LCD and OLED to flexible electronic devices and semiconductor circuits including E-Pper or RFID in addition to color filter and electrode formation.
Compared with photolithography or screen printing, the ink-jet printing technology requires no mask for fine line forming, is not affected by a size of substrate to be printed, and ensures short printing time and simple printing process.
In a conventional printing method for making a color filter, as shown in FIG. 1, ink droplets 2 subsequently discharged from an ink-jet head 1 are hit to a light transmitting region on a transparent substrate 3, and the hit ink droplets, namely a resin composition 2′ is dried to form a pixel pattern.
However, in the conventional printing method, the ink droplets discharged from the ink-jet head and hit to the substrate is spread with isotropy due to a flat surface of the substrate when being surface-contacted with the substrate, so there is a limit in realizing high resolution in lines with fine line widths for enhancing resolution. That is to say, when being hit, the ink droplets may be printed over the line width, which makes the ink droplets blurred.
Meanwhile, for printing a high resolution pattern, it is possible to improve characteristics of ink droplets, but it requires considering complicated factors including dispersion and dynamic viscosity of ink and roughness of a substrate.
That is to say, for ensuring dispersion of ink, there should be considered particle size of coating material, characteristics of additives such as solvent and dispersing agent, and ink characteristics such as ink viscosity and surface tension. Also, after discharging ink, length of ligament like a tail and discharging frequency should be considered, and wettability of ink should also be considered. Thus, there are needed much time and endeavor for pattern printing of high resolution.